The present invention relates to a manufacturing method of a semiconductor device which comprises the steps of forming a copper-containing film, and more particularly to a manufacturing method of a semiconductor device having an interconnection, an interconnection connecting plug, a pad section or such, made of copper or a copper alloy.
In recent years, copper and copper alloys have been widely used as the material for interconnections and connecting plugs to achieve higher speed operations in the elements with these metals utilized, the interconnections and the likes are generally formed by the damascene method.
FIG. 5 is a series of views illustrating the steps of a conventional method of forming a copper interconnection. Now, this method is described below. First, as shown in FIG. 5(a), after an insulating film 10 and an interlayer insulating film 12 are formed, in this order, on a semiconductor substrate (not shown in the drawings), an interconnection trench is set within the interlayer insulating film 12, and thereon a barrier metal film 14 made of Ta, TaN or such and a seed copper film 15 are formed, in succession, and then a copper film 16 is formed by the plating method.
The semiconductor wafer 1 in this state is subjected to the chemical mechanical polishing (CMP) and copper lying outside of the interconnection trench is removed, while copper lying inside of the trench is left as it is, whereby a copper interconnection 17 is formed. At this, copper oxide 21 is produced on the copper interconnection 17, and a carboxylic acid cleaning is performed (FIG. 5(b)) for removing this copper oxide 21. In this way, copper oxide which may cause an increase in interconnection resistance or contact resistance can be eliminated (FIG. 5(c)). After that, as shown in FIG. 5(d), a silicon nitride film 18 is formed and thereon an interlayer insulating film 19 is formed.
In such steps of forming a copper interconnection, it is essential to remove copper oxide which is formed on the copper surface so that the electrical resistance may be prevented from increasing. While copper oxide is removed with carboxylic acid in the above method, other methods such as a method by a plasma treatment with a reducing gas are also known. For example, in a method described in “TDDB Improvement in Cu Metallization under Bias Stress” by J. Noguchi et al. (IEEE 38th Annual International Reliability Physics Symposium, San Jose, Calif., 2000, pp. 339-343), a plasma treatment with a hydrogen or ammonia gas is carried out to achieve the reduction of CuO which is formed on the surface of the copper interconnection to Cu, along with the formation of a Cu layer thereon. Moreover, it is described therein that once CuN is formed, this may function as a protective film, and when a copper-diffusion prevention film of SiN or the like is grown thereon, the CuN layer can suppress the formation of the copper silicide layer in the copper interconnection and, therefore, can restrain the increase in electrical resistance.
However, conventional techniques described above have the following problems.
In a method comprising the step of removing a copper oxide film with carboxylic acid, after the cleaning to remove the copper oxide film is carried out, the wafer is taken out from the cleaning equipment and transferred for the step of growing the films. During -the transfer, the wafer may be exposed to the air so that the copper surface therein may be reoxidized, leading to a problem of the increase in electrical resistance and the decrease in adhesion between the copper interconnection and the copper-diffusion prevention film formed thereon.
Meanwhile, although a method with a reducing plasma treatment can control the increase in resistance in a certain degree, the method brings about another problem of the decrease in interconnection lifetime. In fact, it is the present inventors who first confirmed, through experiments, that a reducing plasma treatment may lower the interconnection lifetime, due to the electromigration or the like, and give rise to a variation in resistance. To remove the copper oxide film thoroughly by the plasma treatment, it is necessary to employ considerably rigorous conditions for the plasma treatment and, as a result, the copper surface becomes rugged. Furthermore, since the nitridation to form CuN proceeds with copper oxide still partially remaining on the copper surface, the film thickness of the CuN becomes non-uniform and, herewith, the film thickness of a copper silicide layer that is to be formed in the copper interconnection becomes also non-uniform. This presumably causes a lowering of the interconnection lifetime and produces variation in resistance.
Further, in the method using the reducing plasma treatment, there are occasions where the film thickness of the copper-diffusion prevention film becomes non-uniform, owing to the unevenness of the underlying layer surface. This necessitates, in the later step of hole etching to form an interconnection connecting plug, to perform overetching further more so as to remove that copper-diffusion prevention film so that the degradation of the copper interconnection surface may be brought about by the plasma exposure.